Write a program that performs a simple n-body simulation, called \"Jumping Lepre

Question

Write a program that performs a simple n-body simulation, called "Jumping Leprechauns." This simulation involves n leprechauns, numbered 1 to n. It maintains a gold value g_i for each leprechaun i, which begins with each leprechaun starting out with a million dollars worth of gold, that is, g_i = 1000000 for each i = 1, 2,...,n. In addition, the simulation also maintains, for each leprechaun, i, a place on the horizon, which is represented as a double-precision floating point number, x_¡. In each iteration of the simulation, the simulation processes the leprechauns in order. Processing a leprechaun i during this iteration begins by computing a new place on the horizon for i, which is determined by the assignment x_i rightarrow x_i + rg_i: where r is a random floating-point number between - 1 and 1. The leprechaun i then steals half the gold from the nearest leprechauns on either side of him and adds this gold to his gold value, g_¡. Write a program that can perform a series of iterations in this simulation for a given number, n, of leprechauns. You must maintain the set of horizon positions using an ordered map data structure described in this chapter.

Explanation / Answer

import java.util.*; public class JumpingLeprechaun implements Comparable { /** * Declaring global variables */ private double x; private double g = 1000000; private JumpingLeprechaun left, right; private int index; /** * Constructor method for JumpingLeprechaun. * Constructs a new JumpingLeprechaun Object based on the given * number on JumpingLeprechaun Objects and the given index. It generates a random * initial horizon value for this specific JumpingLeprechaun Object; sets the * left and right leprechauns to null. * * @param int n - the number of JumpingLeprechaun Objects; * @param int i - the index of the specific JumpingLeprechaun Object created; */ public JumpingLeprechaun(int n, int i) { Random generator = new Random(); double pos = n * generator.nextDouble(); x = pos; index = i; left = null; right = null; } /** * jump method for JumpingLeprechaun. * Calls the setHorizon method with a new horizon value * for the JumpingLeprechaun Object. * * @param double r - a random integer between -1 and 1; */ public void jump(double r) { setHorizon(x + r * g); } /** * setHorizon method for JumpingLeprechaun. * Assigns the JumpingLeprechaun Object's horizon value the received * new horizon value. * * @param double newPos - a new horizon value based on the formula * x + r * g; */ private void setHorizon(double newPos) { x = newPos; } /** * setGold method for JumpingLeprechaun. * Sets the gold of the JumpingLeprechaun Object to the new given value of gold. * * @param double newGold - the new value of gold; */ public void setGold(double newGold) { g = newGold; } /** * getHorizon method for JumpingLeprechaun. * Returns the horizon value of the JumpingLeprechaun Object. * * @return double - the value of the horizon instance variable; */ public double getHorizon() { return x; } /** * getGold method for JumpingLeprechaun. * Returns the gold value of the JumpingLeprechaun Object. * * @return double - the value of the gold instance variable; */ public double getGold() { return g; } /** * getIndex method for JumpingLeprechaun. * Returns the index value of the JumpingLeprechaun Object. * * @return int - the value of the index instance variable; */ public int getIndex() { return index; } /** * visualize method for JumpingLeprechaun. * Returns a String representation of the JumpingLeprechaun Object, * containing the horizon value and the gold value. * * @return String - the String representation of the JumpingLeprechaun Object; */ public String visualize() { return "I am Leprechaun: " + index + ", I am at: " + x + " and I have: " + g + " gold."; } /** * steal method for JumpingLeprechaun. * Method that calls the leftNeighbor and rightNeighbor methods in order to * set the left and right instance variable of the JumpingLeprechaun Object. * It does the "stealing" operations on the left / right neighbors (if they exist), * by incrementing the current JumpingLeprechaun's Object with half of the gold value of * left and right; decreasing the value of gold of left and right to one half. * * @param tm the map in which the Leprechaun is present so that it can find it's relative position */ public void steal(TreeMap tm) { leftNeighbor(tm); rightNeighbor(tm); if (left == null && right != null) { setGold(getGold() + right.getGold()); right.setGold(0); } if (left != null && right == null) { setGold(getGold() + left.getGold()); left.setGold(0); } if (left != null && right != null) { setGold(getGold() + right.getGold()/2 + left.getGold()/2); right.setGold(right.getGold()/2); left.setGold(left.getGold()/2); } } /** * leftNeighbor method for JumpingLeprechaun. * Sets the left neighbor of the current JumpingLeprechaun Object, by giving a * TreeMap Object; it creates a headMap starting with that JumpingLeprechaun Object * as the root and calls the head.lastKey method in order to get the left neighbor. * * @param tm the map in which the Leprechaun is present so that it can find it's own neighbors */ private void leftNeighbor (TreeMap tm) { SortedMap head = tm.headMap(x, false); if (!head.isEmpty()) left = (JumpingLeprechaun)tm.get(head.lastKey()); else left = null; } /** * rightNeighbor method for JumpingLeprechaun. * Sets the right neighbor of the current JumpingLeprechaun Object, by giving a * TreeMap Object; it creates a tailMap starting with that JumpingLeprechaun Object * as the root and calls the tail.firstKey method in order to get the right neighbor. * * @param tm the map in which the Leprechaun is present so that it can find it's own neighbors */ private void rightNeighbor (TreeMap tm) { SortedMap tail = tm.tailMap(x, false); if (!tail.isEmpty()) right = (JumpingLeprechaun)tm.get(tail.firstKey()); else right = null; } public JumpingLeprechaun getRight() {return right;} public JumpingLeprechaun getLeft() {return left;} /** * compareTo method for JumpingLeprechaun. * Implements the compareTo method from Comparable interface. * Compares two horizon values (double). * * @param e the element getting compared for the put method of the TreeMap * @return int - an integer value, based on the different of the compared E Objects; */ public int compareTo(E e) { int myhorizon = (int)x; double ehorizon = (Double)e; int hishorizon = (int)ehorizon; return myhorizon - hishorizon; } }

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